My test board has some customized rootfs, that`s why i failed testing on D series arm.
However, the first part of downgrade procedure was ok: injected lib did the trick and patched everything correctly. TV was able to find lower firmware on usb and initialization of downgrade procedure started successfully. Lib needs to be tested on normal (not customized like mine) D series arm. I bet 99 percent it will work even if in my case TV bricked (explanation above why).

If someone brave enough to try it on D series, i think SamyGO will spend mainboard in case of brick as a compensation. Chance for brick exists, but big chance for success. @erdem_ua ?